The present invention relates a reducing agent for straightening curly hair and a process for straightening curly hair.
In the U.S.A, a cold permanent waving agent having thioglycolic acid as the main component has been studied and developed from around 1940. Thioglycolic acid has been compounded to reducing agents for cold permanent waving, which reduces hair, from the viewpoints that thioglycolic acid is prepared relatively easily, is harmless in terms of health and hygiene, has little odor and maintains favorable waves. Usually, when thioglycolic acid or salts thereof are used as the active ingredient of a reducing agent for waving, high waving strength can be obtained, but the damage to hair is large. Also, when cysteine or salts thereof are used as the active ingredient, the damage to hair is small, but waving strength is weak. To solve such problems, known is a reducing agent, which has a certain waving strength and suppresses damage to the hair, by using thioglycolic acid or salts thereof and cysteine or salts thereof together as the active ingredient and adjusting the pH and alkalinity to a particular range (see JP-A-2002-363041).
However, when this reducing agent is used for straightening curly hair, depending on the curling degree, physical load such as stretching by a comb must be applied, while maintaining the hair in a straight condition under tension. Therefore, according to the above reducing agent, the hair is not sufficiently softened and there is the problem that the desired effects cannot be obtained. Also, to sufficiently soften hair, a preparation having high pH containing a large amount of an alkali agent must also be used and as a result, there is the problem that damage to hair, such as breaking at the roots and removal of cuticles, cannot be reduced.
Also, in the case of hair heavily damaged by coloring, protein in the hair has escaped, thus being more susceptible to external physical influence. As a result, when conducting straightening treatment of curly hair using a comb or a high temperature hair styling iron, the damage received is considerably larger than in the case of permanent waving treatment. In this way, satisfactory effects cannot be obtained by the conventional process for straightening curly hair, due to factors such as the thickness, the curling degree and the degree of damage of hair and the pH of the reducing agent for straightening curly hair.
In order to solve such problems, known is the process for permanently straightening, repairing and styling curly hair using a reducing agent for straightening curly hair that can be easily rinsed off (see Japanese Patent No. 3340999). However, according to this process, the hair is divided into small blocks, the first agent for straightening curly hair is applied to the hair of each block and thereafter, the hair must be wrapped in plastic wrap. Thus, the working efficiency is extremely poor and also, there is the problem that experience is necessary to conduct the process.